Mod 3 - Antibodies Flashcards
What shape does an antibody molecule resemble?
Y shape.
What molecular components are antibodies made of?
Antibodies are glycoproteins that are composed of four polypeptide chains.
How many heavy and light chains do antibodies consist of?
Contains
2 identical heavy chains
2 identical light chains
What are the 5 different classes of antibodies and what are the classes based on?
Based on the heavy chains they possess.
- IgA (alpha)
- IgD (delta)
- IgE (epsilon)
- IgG (gamma)
- IgM (mu)
What do the light chains do and what are the two classes?
Light chains create diversity in the specificity.
Two types of light chains:
1. Kappa (K)
2. Lambda
Is there a functional difference between the two different types of light chains?
No
What light chain is most human antibodies made of?
Kappa chains, 66% of antibody population rather than lambda.
What holds the light and heavy chains together?
Disulfide bonds.
An antibody is a secreted for of an __________.
immunoglobulin, the B cell surface receptor.
What is the portion of an immunoglobulin molecule that attaches to the surface of B cell referred to as?
Transmembrane portion.
What is the constant region?
Region in the immunoglobulin or antibody where there is little variation in the polypeptides between different specificities.
What genes code for the constant region?
The Constant genes (C genes). There are constant genes for each of the heavy chains and light chains.
Now that was hard!
What region of the immunoglobin or antibody contains the antigen binding site? Where is it?
The VARIABLE region at the terminal ends where the antibody binds to the epitope.
The antibody or immunoglobin is symmetric or antisymmetric?
Symmetric.
How many binding sites does one monomer contain because the molecule is symmetric?
One monomer contains two identical binding sites with the same specificity.
What type of chains does the variable region contain?
Variable region is composed of both heavy and light chain regions.
What is the “stem” of an immunoglobulin or antibody called? What does it attach to?
Fc, fragment crystallizable.
Attaches to B cell surface OR
Portion that is recognized and attached to by macrophages for removal of pathogens.
What is the antigen binding site referred to as? Where is it?
Fab region, fragment antigen binding.
Arms of the Y attach to the pathogen.
How do the stem and arms work together to facilitate pathogen removal by a macrophage?
The arms attach to the pathogen, but the stem at the other end is recognized and attached to by the macrophage for the removal of the pathogen that the antibody is specific for.
What is the region where the Fc and Fab regions are held together? Its purpose?
Hinge region.
Allows attachments that vary in distance.
Adds flexibility / efficiency to molecule.
What is the weakness of the hinge region for the immunoglobulin or antibody?
Vulnerable area for enzymes to attack.
Enzymes, e.g. papain and pepsin, can degrade the hinge region and the disulfide bonds, causing the antibody molecule to break up into different Fc and Fab fragments.
If the different classes (or isotypes) of antibodies result in different effector functions but have the same basic structure, what varies between them to have different effector functions?
Different shapes and sizes to allow for a more efficient effector function.
What does the last letter stand for when describing immunoglobulins?
The last letter (capital) represents the heavy chain.
Ig stands for immunoglobulin.
E.g. IgA = immunoglobin alpha
What is the effector function of IgA?
- Mucosal antibody -1st line of defense against pathogens in mucosal membranes.
- IgA2 (dimer) - very efficient neutralizing antibody w/in external secretion of the mucosal membranes (saliva, colostrum, etc.)
What are the two forms of IgA and how many binding site does each have? What special feature are noted?
IgA1 - monomer, 2 binding sites
IgA2 - dimer, 4 identical binding sites, the two monomers are held together with a secretory component (SC), contains a J chain.
J chain is involved in the transepithelium transport of IgA2 to mucosal surfaces and aids to prevent it from degradation.
See Fig 3-9 i notes shown the two forms.
Which form of IgA is present in the circulation?
IgA1 - monomer
What is the function of IgD and where is it typically found?
IgD functions to regulate the activity of B cells. Available in low quantities, but often found on surface of B cells as an immunoglobulin and very rarely seen within the circulation as an antibody.
What two immunoglobulins are displayed on immature B cells?
IgD and IgM
What antibody functions to enhance acute inflammation, protect from parasitic invasions, and is increased in concentrations during allergic reactions?
IgE
Is IgE present in circulation?
Yes, as a monomer.
What does IgE do after secreted by plasma cells? Why?
Attaches to granulocytic cells including: mast cells, eosinophils, and basophils.
These cells contain granules with cytotoxic mediators and cytokines. E.g. mast cells will release histamine in an effect to increase inflammation.
Why is IgE only available in very low quantities?
To prevent hypersensitivity reactions or premature binding to target cells.
What is the most abundant antibody found in intravascular spaces, extravascular spaces, and secretions?
What is unique about this antibody?
IgG, presents as a monomer.
It is so small that it is the only antibody that is able to cross the placenta.
What are the two antibodies capable of fixing complement?
IgG and IgM
How many IgG molecules are required to fix complement?
Two IgG molecules.
How many subclasses does IgG, what are they, and what is the biggest difference between them?
Four subclasses are: IgG1, IgG2, IgG3, and IgG4.
Biggest difference between them is the hinge region. IgG3 has the longest hinge region and is the most efficient at fixing complement.
IgG3>IgG1>IgG2»IgG4
What is the first antibody produced during the primary immune response?
IgM
How does IgM present, number of binding sites?
IgM presents as a pentamer, which means that it has 10 binding sites leading to high avidity
What holds IgM’s monomer’s together?
The five monomers are held together with a J chain (required). This is similar to the J chain that hold the two monomers of IgA2 together, to form the neutralizing dimer found on mucosal surfaces.
How many monomers does IgM have?
5
What does IgM do?
One IgM molecule is able to fix complement as long as it is in the staple form (the antigen binding sites are attached to the
antigens and the Fc portions are raised so that C1qrs can recognize its attachment).
